1. Field of the Invention
This invention relates to horizontal-spindle lathes and more particularly to the frame structures of machines of this type.
2. Description of the Prior Art
Modern horizontal-spindle lathes have two sets of horizontal slides on which two tool-carriages are capable of sliding respectively and independently of each other. The tools can be mounted either directly on the carriages or else on turrets pivotally mounted on said carriages.
Two types of frames are already known, namely those in which a single bed supports the two sets of slides and those in which the two sets of slides are supported respectively by two beds which are rigidly assembled together or which may also form part of a one-piece frame. These known types of frames all have their disadvantages.
In fact, when a single bed carries both sets of slides, all the slides are usually located in the same plane which is inclined to the horizontal at a sharp angle of slope. In consequence, interferences arise in some instances between the paths of the two carriages and simultaneous operation of both carriages is possible only in a certain number of very special cases. It is therefore impossible to determine a program for machining a workpiece without having recourse to layout drawings in order to ensure that the cycle of machining operations as contemplated is really practicable in the case of the machine under consideration.
Lathe frames of the two-bed type are subject to disadvantages which are inherent in their general design principle and also in each particular form of construction. Broadly speaking, the two-bed design is not wholly suitable for the removal of swarf and problems also arise in regard to the protection of some of the slides as well as control and measurement devices.
In a first known two-bed frame arrangement, the two beds are superposed behind the geometrical axis of the lathe spindle, with the result that, in addition to the general drawbacks mentioned in the foregoing, this solution is relatively costly since it entails the need to ensure strictly parallel alignment of the two sets of slides at the time of assembly of these latter on the two beds, that is to say on two separate units. This drawback is removed if the two beds form part of a single-unit frame but the manufacture of a frame of this type is not unattended by practical difficulties.
In a second known arrangement of two-bed frames, the two beds are placed one behind the other on each side of the vertical geometrical plane which passes through the axis of the spindle below the level of said axis. In consequence, the lathe spindle is located between the two carriages and this gives rise to difficulties in loading and unloading of workpieces. Moreover, the tools carried by the rear carriage are not readily accessible and the two carriages have flat horizontal portions which have the undesirable effect of retaining swarf particles.
In a third known arrangement of two-bed frames, one bed is located substantially below the axis of the spindle whilst the other bed is located substantially at the same level as said axis but behind this latter. In other words, the two-bed assembly has a geometrical surface in the form of an inclined plane which slopes downwards in the forward direction. In this solution, the construction of the lower carriage makes it necessary to place the axis of the spindle in a relatively high position, with the result that the spindle is not readily accessible since it is located between the paths of the two carriages. Finally, it is not easy to reach the tools which are mounted on the upper carriage.